Field of the Invention
The present invention relates to an auto-focusing technique during continuous shooting.
Description of the Related Art
Conventionally, techniques for detecting an important object (main object) from an imaging screen are known, and in such techniques, a face identified from features such as a person's eyes and mouth, or a specific object identified from colors and luminance is detected as a main object, for example. Techniques for performing AF (automatic focus) using, as a focusing target, a main object specified by a user from an image displayed on a live view screen via a touch panel or the like are also known.
In addition, as an AF method, a contrast AF method is known, in which a high-frequency component of a luminance signal obtained from an image capturing unit is used as a focus evaluation value, and a position at which this focus evaluation value is a local maximum is used as an in-focus position. In this contrast AF method, a main object detected by the above-described object detection processing is set as a range-finding target area (also referred to as a focus detection area or an AF frame). In addition, as another AF method, a phase difference AF method is known, in which focus detection is performed based on an image signal obtained by an image capturing unit having pixels in which the pupil is divided by an imaging optical system such as a micro-lens. Furthermore, a hybrid AF method in which these two types of AF methods are combined is also known.
Japanese Patent Laid-Open No. 2008-061157 includes a first focusing control unit for performing AF using a phase difference detection method in a plurality of candidate areas in a screen, and specifying a focus detection area from the candidate areas based on a face detection result. A second focusing control unit is further included, which searches for a lens position at which a focus evaluation value in a face area is a local maximum value, based on an output from an image capturing unit, and at least either the first focusing control unit or the second focusing control unit executes a focusing operation.
On the other hand, a technique for updating an in-focus position by performing AF processing for each shooting frame in a camera having a continuous shooting function is known.
Incidentally, in the case of performing AF using a detection result of a main object during continuous shooting, AF cannot be performed until the detection result is obtained, and therefore a frame speed of continuous shooting decreases. In particular, focusing lens driving takes time to control, and if focusing lens is started after the detection result is obtained, there is a risk that the frame speed of continuous shooting will substantially decrease.